The top-ranked Halep's departure is another blow to organisers in the Chinese capital, with Serena Williams missing from the women's draw and several big names also absent from the men's event.

"There is a pain, I couldn't move properly so that's why I stopped," Halep, who suffered a shock early exit from the recent US Open, said.

"I don't know exactly what it is. I will go home, I will have an MRI (scan) and I will see."

"I'm just worried now, I feel sad that I couldn't finish," Halep added, saying that she feared playing was making the problem worse and she knew from the start of the match that she was struggling.

Halep believes it is a different back problem from the one that contributed to her early loss in Wuhan.

"I knew that there is pain, but I thought if I warm up during the match, it's going to be better, but it wasn't," she said.

Holder Caroline Garcia survived a major scare before defeating wildcard Wang Yafan 7-6 (10), 6-7 (4), 6-3 to open the defence of her crown.

The 24-year-old from France defied a rattling roof and a surprisingly stiff challenge from the home player to labour into round two on Beijing's hard courts after more than three hours of nervy action.

Garcia took the first set on a tie-break after 77 minutes during which the retractable roof — which was closed — banged noisily on occasion in the wind.

The fourth-ranked French player and Wang, 78th in the world, went to battle again in the second set and Garcia came back to force another tie-break.

Garcia, who won back-to-back titles last year in China in a breakthrough 2017, rescued one set point in the tie-break but Wang made the second count to force a deciding set.

Garcia was more ruthless this time, racing into a 3-0 lead as the 24-year-old Wang's fighting spirit was finally nullified.

"Compared to the previous year, I didn't take my chances," Garcia said, reflecting on her "disappointing" 2018 compared to her stellar 2017.